This application claims benefit of Japanese Application No. 2002-91939 filed in Japan on Mar. 28, 2002, the contents of which are incorporated by this reference.
1. Field of the Invention
The present invention relates to an image recording apparatus, and more particularly, to an image recording apparatus including a line-type recording head unit formed by connecting a plurality of recording heads and being capable of performing high-speed recording.
2. Description of Related Art
In the art of digital recording apparatuses using an ink-jet recording head (ink-jet printers) or digital recording apparatuses using a thermal transfer recording head (thermal transfer printers), various techniques of correcting density variations in recorded images have been proposed.
One of such techniques is disclosed in U.S. Pat. Nos. 6,045,210 and 6,179,402. In this technique, a recording head of an image recording apparatus comprises a plurality of image recording elements arranged over a range corresponding to a predetermined recording width of a recording medium. In the case of ink-jet printers, for example, variations in shape or other factors among image recording elements (nozzles) of the recording head (printer head) can result in lack of uniformity in size and/or density of recorded dots. Besides, the size and/or density of dots can vary with time. In the image recording apparatus disclosed in U.S. Pat. Nos. 6,045,210 and 6,179,402, in order to solve the above problem, automatic adjustment is made to prevent lack of uniformity in size and/or density of recorded dots and its changes with time.
In order to improve the operation speed and maintainability in conventional image recording apparatuses, an image recording apparatus has been proposed which includes a line-type recording head unit having a plurality of recording heads separated from each other in a width direction of recording medium. A specific example of such an image recording apparatus is a line-head ink-jet printer. In this image recording apparatus, recording elements (nozzles) are disposed on each of the recording heads (print heads), at a pitch corresponding to the resolution on the recording apparatus. In this image recording apparatus, an image is recorded (printed) by scanning relatively to the line-type recording head unit including the plurality of recording heads and the recording medium in a predetermined scanning direction.
In the image recording apparatus disclosed in U.S. Pat. Nos. 6,045,210 and 6,179,402 cited above, the recording density is corrected for each image recording element (nozzle) of a single recording head (print head) included in the image recording apparatus, on the basis of information indicating the number of recorded sheets, the elapsed time, or the like. However, U.S. Pat. Nos. 6,045,210 and 6,179,402 cited above include neither a technical description of correction of a position error caused by lack of uniformity among recording elements of the recording head nor a technical description of correction of a position error which may occur when the recording head is exchanged.
In image recording apparatuses using a line-type recording head unit having a plurality of recording heads, variations in fixing position among recording heads and/or variations in position of recording elements are inevitable. Besides, when one or more recording heads are exchanged for the purpose of maintenance, the exchange may result in a change in fixing position of the one or more recording heads or may result in changes in positions of recording elements. Thus, in order to maintain required high image quality, it is necessary to adjust not only the recording density but also fixing positions of the recording heads and positions of recording elements. In a case in which a single recording head is used, a slight position error or a slight density variation does not have a significant influence on the quality of printed images. However, in a case in which a line-type recording head unit having a plurality of recording heads is used, significant recording positions errors or density variation may result from position errors of recording elements and/or changes in positions due to exchange of recording heads, a temperature change, vibrations (mechanical shock), and/or the like. Thus, it is required to prevent such recording position errors and density variation, in particular, in an area in which nozzles overlap with each other.
It is an object of the present invention to provide an image recording apparatus capable of always recording a high-quality image by automatically correcting position errors of recording heads thereby preventing degradation in image quality which would otherwise occur due to the position errors of the recording heads.
In brief, the present invention provides an image recording apparatus for recording an image onto a recording medium in accordance with an image signal, using a line-type recording head unit including a plurality of recording heads each having a plurality of recording elements disposed in a predetermined direction, the plurality of recording heads being disposed in substantially the same direction as the direction in which the recording elements are disposed, and the plurality of recording heads being disposed such that there is an overlap in recording width between adjacent recording heads. The image recording apparatus comprises test pattern reading means for reading a test pattern image recorded by the respective recording heads; image recording position error detection means for detecting, from the read test pattern, an error in image recording position relative to a predetermined image recording position for each recording element of each recording head; correction data generation means for producing correction data for correcting the error in image recording position for each recording element of each recording head in accordance with the recording position error detected by the image recording position error detection means; correction means for correcting an image signal to be recorded by each recording element of each recording head, on the basis of the produced correction data; and control means for operating the test pattern reading means, the image recording position error detection means, and the correction means at a particular time.
The above and other objects, features and advantages of the invention will become more clearly understood from the following description referring to the accompanying drawings.